Digital electrostatographic printing products are being developed for printing high quality text and half tone images, hence there is a need to formulate electrostatographic toners and developers that produce improved image quality (See Schinichi Sata, et al., STUDY ON THE SURFACE PROPERTIES OF POLYESTER COLOR TONER, IS&T NIP13, 149-152 (1997) and Nash, R. & Muller, R. N. THE EFFECT OF TONER AND CARRIER COMPOSITION ON THE RELATIONSHIP BETWEEN TONER CHARGE TO MASS RATIO AND TONER CONCENTRATION, IS&T NIP 13, 112-10, (1997)). Surface treatment of toners with fumed silica powders, results in toner and developer formulations that have improved powder flow properties and reproduce text and half tone dots more uniformly without character voids (See, Schinichi Sata, et. al., supra). The improved powder fluidity of the toner or developer can however create unwanted print density in white background areas.
The triboelectric charge of electrostatographic developers changes as prints are made, referred to as the "life" of the developer. This instability in charging level is one of the factors that require active process control systems in electrostatographic printers to maintain consistent image-density from print to print.
There is need in the art for developers that are stable with life and that have the advantage of improved electrostatic transfer and higher density capabilities.